An antenna can radiate an electromagnetic wave along a specific direction in a focused way by configuring a maximum antenna size several times larger than or equal to an available wavelength used for the system. Such a structure uses an array of antennas each of which has a maximum direction for radiation of a single electromagnetic wave and features a length of a half wavelength or shorter. When the phases of the electromagnetic waves radiated from the antennas are adjusted, the antennas may be considered to provide a kind of antenna system that focuses electromagnetic waves along the specific direction. The system is generally referred to as an array antenna because the array of antennas is used.
A method of excitation disclosed in JP-2006-245917 A aims at providing a high-frequency substrate capable of fabricating a slot that can easily vary characteristics after the substrate is fabricated. The method uses a pattern configuration and a microstrip line so that the same plane is cyclically provided with conductor cells included in a conductive layer.